Any videos as good introductions to Rugby Union for someone who wants to use this WC to get into watching the sport?
Now that the insanity is over, I'll try answer your question. Have you tried looking on Youtube for any videos? My advice would be to check a couple of those out, watch a game and then ask any questions you can think of in here.
The basics are relatively simple, 15 players per side, 8 on the bench (who are permanent replacements, you can't just interchange them constantly unless there's a concussion test/blood injury) and passes have to go backwards. Tries are 5 points, conversions are 2 points and penalties and drop kicks are 3 points. When a player is tackled with the ball, a ruck is formed around them. If a pass goes forward or the ball is lost forward, a scrum is awarded to the opposite team. If the ball goes out, a lineout is awarded to the opposite team. If a penalty is awarded, the captain gets the choice between a shot at goal, a lineout from a kick or a scrum.